1. Field of the Invention
This invention relates to apparatus for treating slurries containing minerals, soils and sludges which have been contaminated with toxic organic compounds, resulting in their classification as hazardous waste under environmental laws and regulations. More particularly, this invention is directed to an apparatus suited for treating hazardous waste-contaminated solids by means of a bacterial process, i.e., bio-oxidation, at the contaminated site The invention also has applicability to treatment of waste water.
2. Statement of the Art
Within the last decade, public concern regarding environmental pollution issues has increased markedly. As growing industrial activity continues to produce new and more complex waste byproducts, the need for safely disposing of those byproducts poses a critical problem for society. In the area of hazardous waste, this need is especially important in that the particular type of waste constitutes a threat to the health and safety of individuals exposed to them.
Former industry practices have resulted in spills and leaks which have led to the contamination of underground water supplies and surrounding soil. Moreover, past illegal disposal in now-abandoned waste dumps presently poses a threat to the environment and concerns nearby residents. Also, in many industrial facilities, waste water was previously disposed of in unlined lagoons which have leaked and contaminated the groundwater. These lagoons often contain considerable quantities of hazardous waste sludges. There is a pressing need to clean up contaminated waste sites and close existing industrial waste water lagoons.
Several treatment technologies are applicable and can be classified under the general categories of physical, chemical and biological treatment. With respect to biological treatment of soil or sludges, one can differentiate between in situ treatment and the treatment of liquefied soil slurries in reactor vessels. The apparatus of the present invention falls into the latter category.
Presently, several other bioslurry reactor systems are being commercialized The first system, developed by Bogard Environmental Services, Inc. of Mt. Juliet, Tenn. involves technology adapted for use in treating pesticides, PCB's, dioxins and halogenated and nonhalogenated organic compounds. While having presently demonstrated effectiveness for treating sludge, liquids and soils having high organic concentrations, this process has been found to be unsuitable for use with inorganic laden wastes.
The second technology, developed by Detox Industries, Inc. of Sugarland, Tex., is directed for use in treating chlordane, myrex, oil, phenolics, polycyclic aromatic hydrocarbons, creosote, pentachlorophenol (PCP) and polychlorinated biphenyls (PCB's).
The Detox system includes an open reaction tank or on-site created lagoon which utilizes a synthetic liner. The tank is adapted to retain a slurry and is fitted with air distributors.
Another bioslurry reactor consisting of several agitated and aerated vessels has been used in a pesticide spill application by ECOVA of Redmond, Wash.
Common to all three of the above-described systems is the fact that they are operated in a batch mode. After the contaminated soil has been first processed through a classification or soil wash system, the soil and water are placed into the reactor vessel, this slurry is aerated until a desired residual contaminant level is reached, whereupon the supernatant water is usually recycled and the slurry is discharged. Due to the ongoing aeration, many volatile organic substances are not biodegraded but simply are air-stripped. Some systems treat the volatiles in a carbon adsorption filter whereas others simply discharge them to the atmosphere.
Yet another slurry reactor system has been developed by Umwelt Schutz Nord of Ganderkesee, Germany, which system, to the best of our knowledge, employs an inverted trapezoid-shaped reactor and a screw auger at the tank bottom to transport coarser, settling solids. This system may be operated in a continuous mode, but is mechanically complex and expensive to build and operate.
Still another system is under development by the Delft University of Technology of The Netherlands. The Delft design employs two reactors in series, the first of which also acts as a separator from which the coarser, settled particles are transported directly to a dewatering system into which the finer particles are transported after treatment in the reactors. The system maintains the contaminated solids in a three-phase (solid-liquid-gas) slurry suspension in a fluidized bed. While effective, such a design requires a great deal of energy to maintain the suspension during the bioreaction process. In addition, the Delft design employs reactor vessels with a steeply sloped lower hopper portion (60.degree. from horizontal) which greatly increases the height of the reactor vessel for a given volume.
Both of the foregoing systems have apparently been designed for transport to the contaminated site and for use in conjunction with a soil washing pretreatment step which reduces the volume of soil to be treated in the bioslurry reactor. Such methodology being part of the prior art, and not a part of the present invention, no further description thereof will be made.
Common to all hazardous waste treatment systems utilizing bacterial activity is the requirement of providing an adequate supply of oxygen and nutrients to the bacteria. This provision allows biomass growth and facilitates the occurrence of biochemical reactions, thereby leading to the production of carbon dioxide and water as final products
The clean up of hazardous waste sites requires innovative approaches that are cost effective. As has been the case in the waste water treatment sector, biological systems can also play an important role in soil bioremediation. It is important to develop reactor vessels and processes that can achieve high biokinetic degradation rates in order to handle high solids concentrations and large throughput volumes.
In addition, it has been determined that there are many contaminated sites in which the volume of contaminants does not justify the erection of a large volume, permanent type of system, but in which the volume of contaminants renders transport of same to a remote site impractical, even after consolidation of the contaminants in a smaller volume. As previously noted, transportable systems have been under development, but suffer from major deficiencies insofar as manufacturing and operating costs are concerned.